Add companion edition mapping API endpoint (closes #2929)

[Adarshkumar0509]

Description

The companion edition mapping data was accessible internally but not exposed via the public API. This PR wires up the missing configuration to make /api/mapping/companion/1.0 available as a public endpoint.

Changes made:

• svelte.config.js I added prerender entry for /api/mapping/companion/1.0
• headers.js and headers-stage.js then added CORS headers for the new endpoint
• openapi.yaml added /mapping/companion/{version} endpoint documentation

No new route file was needed as the existing dynamic [edition]/[version] route and MappingService already handle the companion edition.

fixed issue: #2929

Screenshot

before it was missing companion endpoint

after

AI Tool Disclosure

• My contribution includes AI-generated content, as disclosed below:
  • AI Tools: Claude
  • LLMs and versions: Claude Sonnet 4.6
  • Prompts: Asked Claude to help verify my changes and approach were correct

Affirmation

• My code follows the CONTRIBUTING.md guidelines

[Adarshkumar0509]

hii @sydseter please take a look at this whenever you have time.